The overall objective of this study is to understand the control of contraction/relaxation of the uterus at the molecular level. To achieve these goals, the ability of uterine relaxants to attenuate contractant- induced phosphoinositide turnover via the action of second messengers will be tested. This will be achieved with the use of protein kinase A and C inhibitors. The effect of several uterine relaxants on Ca extrusion and microsomal uptake will be determined, using both direct and indirect assays, and the role of protein kinase A in relaxant- induced reductions in intracellular calcium assessed. An attempt will be made to define the characteristics of K and Ca channels in the muscle layers of the myometrium, using indirect vesicle assays, membrane potential indicators, channel reconstitution into lipid bilayers, and patch clamp methodology. The role of GTP-binding proteins in the operation of these channels and the influence of contractants and relaxants will be studied. The effect of several uterine relaxants on myosin light chain kinase activity will be determined. The effect of hormonal manipulation and pregnancy on the properties of uterine K and Ca channels and their hormonal regulation and on the expression of phospholipase C mRNA will be studies. These studies should provide new insight into the biochemical mechanisms by which contractants and relaxants interact with the uterus.